I know the best way to know why your check engine light is to just hook up the scanner and get the code, but my friend that has a scanner is out of town for a week an I don't have very good patience when it comes to truck issues. Anyways, when I drive my 04 Silverado around all is well until I get to about 50mph. My check engine light will come on and I'm not sure why. There isn't a change in the way it is running at all. It doesn't become sluggish or anything. I read that if you disconnect your battery cables for 30 minutes it resets your codes so I did that. Sure enough, when I turned the truck back on the Check Engine Light was off. However, next time I got about 50 mph it came back on. Didn't change a bit how it was running and I can drive it around town at 30 or 40 for quite awhile without ever noticing it. Anyone have any ideas? I bought the truck at an auction and the Check Engine Light was on when I got it and I've done some work on it sense then. Should I just reset the codes with a scanner and see what happens? Maybe just disconnecting the battery cables for an hour or so doesn't completely reset things?

Like I said, just curious and I know the best route to go is just wait on my friend to get home, but I'm anxious to know asap!! Wondering if anyone else had anything similiar.

 

i would have it scanned to see what code it is not all them make the engine run different if you live near an autozone they will scan it for free harbor freight sells some cheap ones that you can read the codes and erase them i'v never tried the battery disconnect way

Sean

97 4x4 burb

 

It could be something as simple as a clogged fuel fill vent line or just leaving your gas cap off will cause it to do that. I was told if it was your gas cap you need to use the ignition about 200 times before it clears, unless you get someone to clear it with a computer. Anyway if you did some recent fourwheeling, it could be the fuel vent.

 

Have it scanned. You will probably never figure it out unless you do.

 

I am currently having the same problem, kinda. I have not really noticed it relates to speed, but more to the bumps in the road. I live off a 2mi dirt road that has many ruts. Seems if I hit a rut too hard or hit a large bump at hiway speeds, it triggers the engine light. I however, have had the light checked. Codes as follows:
P0101
P0171
P0174
the first is "MAF sensor performance"
second, "Fuel trim system lean at upstream oxygen sensor(left cylinder bank)"
third, Fuel system trim lean at upstream oxygen sensor(right cylinder bank)

Was told that the MAF has not failed, that there is a leak upstream between MAF and O2 sensors, and the lean fuel mixture would agree with this. I have not been able to find any leaks or pin holes in the air tube between sensors, and cleaned the connections for the air tube. I was wondering if the aftermarket K&N air filter installed might have something to do with my problems(possibly allowing more air than MAF can read?)

Any help would be greatly appreciated

 

i've heard of oil from the filters getting on the MAF sensor and causing some problems, the MAF can be cleaned,ive had the 171 and 174 code on my ford windstar it was the upper intake manifold gaskets, you have a loose conncetion or air getting in after the MAF some where that the computer can't compensate for, i would clean the MAF,check for any loose connections and then if it comes back i would change the upper intake gaskets i think places like autozone sell a kit



Sean

97 4x4 burb

 

Well, mine ended up being the engine coolant sensor and knock sensors that were triggering the check engine light. The engine coolant sensor was a cheap and easy fix. Not sure yet on the knock sensors. I'm going to start another thread for the knock sensors so I can get some feedback on how to repair.

 

are you meaning the gaskets for the intake manifold?

Checked and blew out the MAF. Checked the upper air tube, and couldnt find cracks or holes, and fittings are in good shape. still having CEL but not noticing engine running rough. Next choice is looking for a high performance MAF to see if that works.